I know they mentioned them as a future release, but why, then, are they not present on the existing career cards? If it's not still too late, you guys at FFG should include them in the heading texts along with the other races, with a note in the box that they will be present in future expansions.
I would think having separate cards for the halflings would be slightly ridiculous. An errata chart or replacement cards would be both time and space wasted (having to check the chart for valid careers is counter to the whole reason you have the cards).
Perhaps making things with the future releases in mind will help make the product more professional, polished, and playable, as that was the ostensible goal of a new edition?
Dwarf, Halfling and a Human Midget party. That would be a sight... What else, maybe a former Pygmie Slave from Lustria or the Southlands. If there only would be Gnomes still in the Warhammer World...